1. Field of the Invention
The present invention relates to for testing the driving of nozzles in an ink-jet printer which is capable of informing a user of a defect of a nozzle or the number of defective nozzles, by testing the driving state of each nozzle through the variation of the voltage generated by a nozzle driving unit when the nozzles are driven successively.
2. Description of the Related Art
An ink-jet printer is an apparatus which records data by spreading ink on a paper. The ink-jet printer includes a printer head having a number of nozzles for spreading ink, and the printer head is usually located in an ink cartridge where ink is stored.
Such a printer includes a nozzle driving unit for driving a number of nozzles of the printer head. The nozzle driving unit drives the nozzles by receiving a nozzle driving signal generated by a control unit.
Exothermic resistances for heating the ink of each nozzle in the printer head are provided. Each of the exothermic resistances is connected in series with each of the respective nozzle driving transistors. The exothermic resistances are connected to a head driving power supply having a power supply voltage of 24 volts, for example, by means of separate resistances for each group.
The nozzle driving transistors are turned on as the nozzle driving signal generated by the control unit is supplied to each base terminal of the driving transistors. As a result, the exothermic resistance corresponding to the turned on transistor is provided with a current to generate heat.
Due to the heat generated, ink is heated, and in turn, bubbles are produced. As the bubbles expand, ink spurts out of the nozzle to produce a dot on paper.
The ink-jet printer drives a carriage return motor and moves the ink cartridge to the right and left to produce a multiplicity of dots on a paper to form a word or a graphic.
However, when the ink cartridge is used for a long time, the circuit of the nozzle driving unit which is electrically sensitive can be damaged, and the quality of printing is lowered, as ink is not spread from some nozzles.
In these cases, in order to test for the driving state of the nozzles, a user can confirm the printing state by outputting a test pattern of a predetermined form, via an application program for nozzle testing which is performed in a computer or a self test program provided in the printer itself. However, these methods have disadvantages in that the user must know the operation method of the test program and the user must manually confirm the driving state of the nozzles.
The patent to Ikeda et al., U.S. Pat. No. 5,319,389, entitled Method Of Abnormal State Detection For Ink Jet Recording Apparatus, discloses a method in which the resistance of the heating resistors for the nozzles are measured to determine abnormalities therein.
The patent to Hayashi, U.S. Pat. No. 5,608,333, entitled Method Of Driving Heating Element To Match Its Resistance, Thermal Printer, And Resistance Measuring Device, discloses a method in which the resistance value of each heating element in a thermal printer is indirectly measured.
The patent to McSparran et al., U.S. Pat. No. 4,996,487, entitled Apparatus For Detecting Failure Of Thermal Heaters In Ink Jet Printers, measures the resistance of the resistive heater element in a printer and generates a failure signal when a resistance is determined to be above a preselected value.
The following additional patent each disclose features in common with the present invention but are not as pertinent as the patents noted in detail above: U.S. Pat. No. 5,521,620 to Becerra et al., entitled Correction Circuit For An Ink Jet Device To Maintain Print Quality, U.S. Pat. No. 4,907,013 to Hubbard et al., entitled Circuitry For Detecting Malfunction Of Ink Jet Printhead, U.S. Pat. No. 5,206,668 to Lo et al., entitled Method And Apparatus For Detecting Ink Flow, U.S. Pat. No. 5,428,376 to Wade et al., entitled Thermal Turn On Energy Test For An Inkjet Printer, U.S. Pat. No. 5,418,558 to Hock et al., entitled Determining The Operating Energy Of A Thermal Ink Jet Printhead Using An Onboard Thermal Sense Resistor, U.S. Pat. No. 5,627,572 to Harrington III et al., entitled Programmable Head Type Detection And Maintenance System, U.S. Pat. No. 5,539,434 to Fuse, entitled Ink Jet Recording Apparatus And Method Therefor, U.S. Pat. No. 5,526,027 to Wade et al., entitled Thermal Turn On Energy Test For N Inkjet Printer, U.S. Pat. No. 5,638,097 to Taskayanagi et al., entitled Recording Apparatus To Which Recording Head Is Detachably Mounted, and U.S. Pat. No. 5,576,745 to Matsubara, entitled Recording Apparatus Having Thermal Head And Recording Method.
While each of the aforecited patents disclose features in common with the present invention, none of these patents teaches or suggests the specifically recited technique for testing the driving of nozzles in an ink-jet printer in accordance with the present invention.